The present invention relates to an apparatus and method for obtaining samples at different levels from within oil containers such as an oil storage tank or a cargo tank of an oil tanker, in order to accurately determine the level of water in such a tank, the remainder of the tank being filled with oil and thereby to determine the level of the water/oil interface therein.
It often occurs that oil which is loaded into oil tanks of oil tankers at ports contains substantial quantities of water. This is because water was produced or obtained during the oil drilling process, and was loaded aboard the tanker along with the crude oil. Also, water may already be within such a cargo tank, because of leakage into the tanks or because the water was inadvertently left in the tanks when the tanks were filled with sea water which was used for ballast.
The purchaser of such oil loaded aboard a tanker wishes to determine the exact quantity of water within a tank otherwise filled with oil, and wishes to determine the chemical nature of the water, which may be determined by taking a sample of such water. A determination of the nature of such water will help determine its source. Furthermore, such a buyer may be required to pay only for the oil placed aboard the tanker and not the water, and the transporter of the oil cargo may desire to check such tanks himself. Hence, accurate water-oil interface determinations in such tanks are likely to be economically valuable.
It is already known in this art to lower a sampling bob to the bottom of the liquid-filled tank, either a storage tank or within an oil tanker, to obtain samples of such liquids at various levels, and thereafter to test such samples to determine whether at any given level, water or oil is present. However, the art requires an apparatus and method for utilizing such bobs to determine water levels in such tanks quickly and efficiently and in a manner so that the results are reliable, and requires improved sampling bobs for use with such apparatus. Patent application Ser. No. 937,293, filed Aug. 28, 1978, entitled "Method And Apparatus For Obtaining A Selective Liquid Sample From Near The Bottom Surface Of A Liquid-Filled Tank", assigned to Mobil Oil Corporation, shows a prior sampling bob and system.